[fpc-pascal] How can I get a typeinfo by address?

Michael Van Canneyt michael at freepascal.org
Fri Jul 17 16:33:52 CEST 2015

On Fri, 17 Jul 2015, silvioprog wrote:

> Hello,
> I need to call a method dynamically by its name over string and pass some parameters to it. OK, I don't know if it is possibly in the current version of the compiler, but I'm trying to do something
> like this:
> TMethodInvoker.Invoke(VMyObj, ['Param 1', 'Param 2', 1, True]);
> I already get some paramerter informations using this code[1], that prints all parameters and its types using RTTI.
> So I have a question: how can I get the method typedata looking for it in the VMT? Please see this:
>   WriteLn(HexStr(@TMyObject.Test));
>   WriteLn(HexStr(TMyObject.MethodAddress('Test')));
> Prints the same address. But:
>   TI := TypeInfo(@TMyObject.Test);
>   WriteLn(HexStr(TI));
>   TI := TypeInfo(TMyObject.MethodAddress('Test'));
>   WriteLn(HexStr(TI));
> Prints different results.

You cannot get typeinfo like that for methods.
You need to call GetPropInfo() from the typeinfo unit for published properties/methods.

> How System.TypeInfo retrieve the typeinfo from my @TMyObject.Test address? It is done by the method address so?


> I took a look at the TRTTIWriter class and also in the VMT, but I don't know how the compiler handles this informations internally, so sorry it this question sounds nonsense. =P

You can check the reader class in classes unit.


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